Parking devices of such a type have heretofore been developed, each of which includes a piston, a housing accommodating the piston, and a solenoid valve that moves the piston in the direction of releasing a parking lock against an elastic force of a spring by supplying hydraulic oil from a mechanical pump to a hydraulic oil chamber defined by the piston and the housing (refer to Patent Document 1, for example). To move the piston in the direction of releasing the parking lock and hold the piston in the released state of the parking lock, this parking device supplies the hydraulic oil from the mechanical pump to the hydraulic oil chamber via the solenoid valve. To move the piston in the direction of applying the parking lock, the parking device discharges the hydraulic oil from the hydraulic oil chamber via the solenoid valve.